Clamping device for tool holder

ABSTRACT

A clamping device for releasably holding a tool holder shank includes a housing, a drawbar axially moveable in a bore in the housing between an advanced releasing position and a retracted locking position, engagement members moveable under the effect of the drawbar into locking engagement with the tool holder shank, and a sleeve arranged around a wall of the housing and axially moveable in relation to it. A first wedge is received in a first aperture in the wall and configured to move the drawbar rearwards in the bore when pressed radially inwards in the aperture by movement of the sleeve in a first axial direction. A second wedge is received in a second aperture in the wall and configured to move the drawbar forwards in the bore when pressed radially inwards in the aperture by movement of said sleeve in an opposite axial direction.

FIELD OF THE INVENTION AND PRIOR ART

The present invention relates to a clamping device according to thepreamble of claim 1, which is intended to be used for connecting a toolholder to a machine tool.

Within the field of machine tools for metal cutting, the cutting tools,for instance in the form of drills, milling tools or lathe tools, usedfor machining work pieces of metallic material are often fixed to a toolholder, which in its turn may be detachably fixed to a clamping devicethat is mounted to a machine tool. It is previously know to clamp ashank of such a tool holder to the housing of a clamping device by meansof a clamping mechanism arranged in the housing. Tool holders forcutting tools in the form of drills and milling tools are normallyclamped to a rotatable housing in the form of a spindle, whereas toolholders for lathe tools may be clamped to a non-rotatably arrangedhousing. When the cutting tool needs to be exchanged, the tool holder isreleased from the housing of the clamping device and a new tool holderwith another cutting tool is clamped to the housing. A clamping deviceof this type may for instance be detachably fixed at the periphery of atool turret included in a machine tool.

A clamping device comprising a spindle with a clamping mechanism adaptedfor an automatic tool changing operation is previously known from EP 1468 767 B1. In the clamping device according to EP 1 468 767 B1, anactuating member in the form of a first drawbar is slidably mountedinside the spindle and configured to effect an axial displacement of asecond drawbar via a force amplifying mechanism comprising a number ofco-operating wedges arranged between the drawbars. A gas spring insidethe spindle is configured to urge the two drawbars into a retractedlocking position, in which a tool holder is clamped to the spindle, anda hydraulic piston may be configured to act on a piston at the rear endof the gas spring in order to achieve a displacement of the two drawbarsinto an advanced releasing position, in which the tool holder may bereleased from the spindle. However, this previously known clampingdevice has a relatively long axial extent and it is therefore notsuitable to use this type of clamping device when tool holders are to bedetachably fixed at the periphery of a tool turret where the availableaxial space for the clamping device is limited.

OBJECT OF THE INVENTION

The object of the present invention is to provide a clamping device ofthe above-mentioned type that has a new and favourable design and thatis suitable for use with a tool turret of a machine tool.

SUMMARY OF THE INVENTION

According to the invention, said object is achieved by means of aclamping device having the features defined in claim 1.

The clamping device according to the invention comprises:

-   -   a housing having a front end, a rear end and a bore which        intersects the front end and extends rearwardly therefrom,        wherein a mounting portion for receiving the tool holder shank        is provided at a front end of the bore;    -   a drawbar slidably mounted inside the bore so as to be        reciprocally moveable in the bore along a longitudinal axis        thereof between an advanced releasing position and a retracted        locking position;    -   engagement members arranged around the drawbar at a front end        thereof, wherein the engagement members, under the effect of a        movement of the drawbar from the advanced releasing position to        the retracted locking position, are moveable from a first        position, in which the engagement members allow the tool holder        shank to move into and out of said mounting portion of the bore,        to a second position, in which the engagement members are in        locking engagement with the tool holder shank and keep it        secured to the housing;    -   a first wedge slidably received in a first aperture that extends        radially through a peripheral wall of the housing, wherein the        first wedge comprises a first wedge surface, which faces towards        the rear end of the housing and is in contact with a first slide        surface on the drawbar facing towards the front end of the        housing, and a first pressure receiving surface, which faces        outwards from the housing, the first wedge being configured to        press the drawbar towards the retracted locking position when it        is pressed radially inwards in the first aperture;    -   a second wedge slidably received in a second aperture that        extends radially through the peripheral wall, wherein the second        wedge comprises a second wedge surface, which faces towards the        front end of the housing and is in contact with a second slide        surface on the drawbar facing towards the rear end of the        housing, and a second pressure receiving surface, which faces        outwards from the housing, the second wedge being configured to        press the drawbar towards the advanced releasing position when        it is pressed radially inwards in the second aperture; and    -   an actuating sleeve arranged around the peripheral wall and        slidably mounted to it so as to be axially moveable in relation        to the housing in a first axial direction in order to effect a        movement of the drawbar from the advanced releasing position to        the retracted locking position and in an opposite second axial        direction in order to effect a movement of the drawbar from the        retracted locking position to the advanced releasing position,        wherein the actuating sleeve on its inner side is provided with        a first pressure applying surface, which faces inwards for        contacting the first pressure receiving surface and has a radial        distance to the longitudinal axis that increases as seen in said        first axial direction, and a second pressure applying surface,        which faces inwards for contacting the second pressure receiving        surface and has a radial distance to the longitudinal axis that        increases as seen in said second axial direction.

The first pressure applying surface of the actuating sleeve isconfigured to press the first wedge radially inwards in the firstaperture by pressing against the first pressure receiving surface whenthe actuating sleeve is moved in said first axial direction. The secondpressure applying surface of the actuating sleeve is configured to pressthe second wedge radially inwards in the second aperture by pressingagainst the second pressure receiving surface when the actuating sleeveis moved in said second axial direction. Thus, the drawbar is moveablefrom the advanced releasing position to the retracted locking positionunder the effect of the actuating sleeve and the first wedge by movementof the actuating sleeve in said first axial direction, and the drawbaris moveable from the retracted locking position to the advancedreleasing position under the effect of the actuating sleeve and thesecond wedge by movement of the actuating sleeve in said second axialdirection.

Since the first pressure applying surface of the actuating sleeve has aradial distance to the longitudinal axis that increases in the firstaxial direction, a movement of the actuating sleeve in the first axialdirection will cause a pressure to be applied by the first pressureapplying surface on the first pressure receiving surface on the firstwedge. This pressure will have a component in the radial direction suchthat the first wedge is pressed radially inwards towards thelongitudinal axis.

Since the second pressure applying surface of the actuating sleeve has aradial distance to the longitudinal axis that increases in the secondaxial direction, a movement of the actuating sleeve in the second axialdirection will cause a pressure to be applied by the second pressureapplying surface on the second pressure receiving surface on the secondwedge.

This pressure will have a component in the radial direction such thatthe second wedge is pressed radially inwards towards the longitudinalaxis.

By using the above-mentioned actuating sleeve for controlling the axialmovement of the drawbar, no gas spring or the similar that takes up alot of space in the axial direction is required for controlling theaxial movement of the drawbar, which implies that the clamping devicecan be made compact in axial direction. The clamping device is thereforesuitable for use in tool turrets. Furthermore, the use of separatewedges for controlling the axial movement of the drawbar in the twodifferent directions implies that the design of the first wedge can beoptimized to suit the specific requirements associated with the movementof the drawbar from the advanced releasing position to the retractedlocking position and that the design of the second wedge can beoptimized to suit the specific requirements associated with the oppositemovement of the drawbar from the retracted locking position to theadvanced releasing position.

The above-mentioned housing of the clamping device may have the form ofa rotatable spindle, which may be connected or connectable to a drivemechanism in a tool turret of a machine tool. However, the clampingdevice of the present invention is not limited to use in a tool turret,and such a housing in the form of a rotatable spindle could as analternative constitute the main spindle of a machine tool or beconnected to such a main spindle without any intermediate tool turret.When the housing has the form of a rotatable spindle, the clampingdevice may be used for clamping tool holders provided with drilling ormilling tools or other types of rotating tools. The housing included inthe clamping device of the present invention may as a furtheralternative be a non-rotatable housing. In the latter case, the clampingdevice may be used for clamping tool holders provided with lathe toolsor other types of non-rotating tools.

According to an embodiment of the invention, the actuating sleeve isconfigured to assume a self-locking axial position on the peripheralwall of the housing when the drawbar has been forced into the retractedlocking position under the effect of the actuating sleeve and the firstwedge, so as to thereby keep the drawbar in the retracted lockingposition. Hereby, the actuating sleeve is capable of keeping the drawbarin the retracted locking position without requiring any external forcefrom an actuator, which implies that the actuating sleeve only needs tobe subjected to external force from an actuator, for instance in theform of a hydraulic or pneumatic actuator, in connection with a toolchanging operation.

According to another embodiment of the invention, the first pressureapplying surface and the first pressure receiving surface are inclinedin relation to the longitudinal axis by such an angle α that the firstwedge will keep the actuating sleeve in a self-locking axial position onthe peripheral wall when the drawbar has been forced into the retractedlocking position under the effect of the actuating sleeve and the firstwedge. In this case, the first pressure applying surface and the firstpressure receiving surface both extend in the same direction when viewedin a longitudinal section through the housing. The angle α is chosen soas to be below a self-lock threshold angle, such that the actuatingsleeve attains a self-locking axial position in relation to the firstwedge when the drawbar has been displaced inside the bore into theretracted locking position. To obtain a self-locking axial position, theangle α should be sufficiently small, i.e. below the self-lock thresholdangle. A self-locking axial position refers to an axial position inwhich the static frictional force between the first pressure receivingsurface on the first wedge and the first pressure applying surface onthe actuating sleeve is greater than the opposing force in the plane offriction that is caused by a force applied to the first wedge in aradial direction perpendicular to the longitudinal axis. Hence, aself-locking axial position is obtained within an angular range thatdepends on the coefficient of friction between the first pressurereceiving surface on the first wedge and the first pressure applyingsurface on the actuating sleeve. This coefficient of friction depends onvarious parameters, such as the materials used, coatings on thesurfaces, use of lubricants, etc. Hence, the self-lock threshold angleis dependent on such parameters. A person skilled in the art will beable to identify the self-lock threshold angle that apply in eachspecific case by using common general knowledge and/or routineexperiments, or at least predict or assess whether a certain angle isbelow such a self-lock threshold angle. In general, it is preferred tochoose an angle α that is well below the self-lock threshold angle, tothereby ensure a self-locking configuration. A further benefit of usinga small angle α is that a force-amplifying effect is achieved, owing tothe fact that a small angle α implies that a relatively long axialdisplacement of the actuating sleeve will result in a relatively shortaxial displacement of the drawbar. However, a too small angle α may beinefficient and not practically well-functioning. For example, a verysmall angle α may render it difficult to release the actuating sleevefrom the self-locking axial position. The angle α is with advantagebetween 2° and 10°. With an angle α within this range, a self-lockingeffect as well as an appropriate force-amplifying effect may beachieved.

Another embodiment of the invention is characterized in:

-   -   that the first wedge comprises a third pressure receiving        surface which faces outwards from the housing;    -   that the actuating sleeve on its inner side is provided with a        third pressure applying surface which faces inwards for        contacting the third pressure receiving surface, the third        pressure applying surface having a radial distance to the        longitudinal axis that increases as seen in said first axial        direction;    -   that the third pressure applying surface and the third pressure        receiving surface are inclined in relation to the longitudinal        axis by an angle β which is larger than the angle α; and    -   that the first and third pressure applying surfaces and the        first and third pressure receiving surfaces are arranged        consecutively on the actuating sleeve and on the first wedge,        respectively, such that, upon a movement of the actuating sleeve        in the first axial direction, the third pressure applying        surface is configured to slide and press against the third        pressure receiving surface on the first wedge during a first        phase of the movement and the first pressure applying surface is        configured to slide and press against the first pressure        receiving surface on the first wedge during a subsequent second        phase of the movement.

Hereby, the drawbar may be quickly moved in axial direction during theinitial phase of the clamping under the effect of the larger angle β.This initial clamping phase does not require much force. However, duringthe final phase of the clamping, a great force is required fordisplacing the drawbar a short distance.

When the actual clamping occurs, i.e. when the engagement members assumethe above-mentioned first position, the drawbar is moved in axialdirection under the effect of the smaller angle α such that the axialmovement of the drawbar will be small as compared to the axial movementof the actuating sleeve, which results in a force-amplifying effect,also referred to as “power boost”. The angle β is suitably between 10°and 75°, preferably between 35° and 65°, which provides an efficientinitial axial movement of the drawbar. By using a steep angle β for theinitial axial movement of the drawbar and a small angle α for the actualclamping, the actuating sleeve (and thus the entire clamping device) canbe made relatively short in the axial direction while still providing aself-locking clamping mechanism with a significant force-amplifyingeffect.

According to another embodiment of the invention, the first and thirdpressure applying surfaces and the first and third pressure receivingsurfaces are curved as seen in a cross-sectional plane perpendicular tothe longitudinal axis, which will facilitate the manufacturing of theactuating sleeve.

According to another embodiment of the invention, the first pressureapplying surface and the second pressure applying surface partly overlapeach other in the axial direction of the actuating sleeve and are spacedapart from each other in the circumferential direction of the actuatingsleeve. The length of the actuating sleeve may hereby be reduced.Furthermore, the second pressure applying surface is with advantageprovided in a recess formed in a rotationally symmetric inner wallsurface of the actuating sleeve.

According to another embodiment of the invention, the clamping devicecomprises two or more such first wedges spaced apart in thecircumferential direction of the peripheral wall, wherein each firstwedge is received in a respective first aperture that extends radiallythrough the peripheral wall. The clamping device may also comprise twoor more such second wedges spaced apart in the circumferential directionof the peripheral wall, wherein each second wedge is received in arespective second aperture that extends radially through the peripheralwall. The first apertures and the associated first wedges, as well asthe second apertures and the associated second wedges, are preferablyevenly distributed in the circumferential direction of the peripheralwall. Hereby, a well-balanced clamping device with good forcedistribution is obtained. A very high number of wedges and associatedapertures may however be unfavourable, owing to the fact that eachaperture will reduce the strength of the housing. Three first wedges andthree second wedges with associated apertures will give a well-balancedclamping device with a suitable level of force distribution, while stillmaintaining a sufficient strength of the housing. The first wedges andthe second wedges are with advantage alternately arranged as seen in thecircumferential direction of the peripheral wall, wherein each one ofthe first wedges is followed by one of the second wedges as seen in thecircumferential direction of the peripheral wall and each one of thesecond wedges is followed by one of the first wedges as seen in thecircumferential direction of the peripheral wall.

Further advantageous features of the clamping device according to thepresent invention will appear from the description following below andthe dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the appended drawings, a specific description ofembodiments of the invention cited as examples follows below. In thedrawings:

FIG. 1 is a lateral view of a clamping device according to an embodimentof the present invention, with a tool holder clamped to the housing ofthe clamping device,

FIG. 2 is a longitudinal section through the clamping device and toolholder shown in FIG. 1 , with the drawbar of the clamping device in aretracted locking position and with the tool holder clamped to thehousing,

FIG. 3 is a partly cut perspective view of the clamping device of FIG. 1,

FIG. 4 is a longitudinal section corresponding to FIG. 2 ,

FIG. 5 is a longitudinal section through the clamping device and toolholder shown in FIG. 1 , with the drawbar in an advanced releasingposition,

FIG. 6 is a longitudinal section through the clamping device and toolholder shown in FIG. 1 , with the drawbar in an intermediate positionbetween the advanced releasing position and the retracted lockingposition,

FIG. 7 is an exploded view of the clamping device and tool holder ofFIG. 1 ,

FIG. 8 is an exploded view from another direction of the clamping deviceand tool holder of FIG. 1 ,

FIG. 9 is a cross-section according to the line IX-IX in FIG. 4 ,

FIG. 10 is a cross-section according to the line X-X in FIG. 4 , and

FIG. 11 is a cross-section according to the line XI-XI in FIG. 4 .

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

A clamping device 1 according to an embodiment of the present inventionis illustrated in FIGS. 1-10 . The clamping device 1 is configured toreleasably clamp a tool holder 60 (very schematically illustrated in thedrawings) to a housing 2 of the clamping device and enable the machiningof a work piece by means of a cutting tool (not shown) fixed to the toolholder 60.

The housing 2 has a front end 2 a, a rear end 2 b and a bore 3 whichintersects the front end 2 a and extends rearwardly therefrom. Thus, thebore 3 has an entrance opening 3 a (see FIG. 3 ) at the front end 2 a ofthe housing. The housing 2 is connectable to a tool turret of a machinetool via a connection member 4, which extends from the housing 2 at therear end thereof.

In the illustrated embodiment, the housing 2 has the form of a machinespindle, and this spindle-shaped housing 2 may be rotatably mounted in asurrounding casing by means of rolling bearings. In this case, thehousing 2 may be connectable to a drive mechanism of a machine tool, forinstance a drive mechanism in a tool turret of a machine tool, via theconnection member 4 in order to allow the housing 2 to be driven inrotation by the drive mechanism. However, the housing 2 may as analternative be designed as a non-rotatable housing.

A drawbar 5 is slidably mounted inside the bore 3 of the housing 2 so asto be reciprocally moveable in the bore 3 along a longitudinal axis Lthereof between an advanced releasing position (see FIG. 5 ) and aretracted locking position (see FIGS. 2 and 4 ). The drawbar 5 has afront end facing the entrance opening 3 a of the bore 3 and an oppositerear end. A head portion 6 and a neck portion 7 are provided at thefront end of the drawbar 5. The head portion 6 is located in front ofthe neck portion 7 as seen in the longitudinal direction of the drawbar,wherein the head portion 6 is connected to the neck portion 7 via arearwardly facing bevelled surface 8 on the head portion 6. A sealingring 9 is arranged between the drawbar 5 and an inner surface of thebore 3. In the illustrated example, this sealing ring 9 is received in agroove on the outer side of the drawbar 5.

The drawbar 5 is prevented from rotating in relation to the housing 2.In the illustrated embodiment, two planar wall sections 5 c, 5 d (seeFIGS. 2 and 9 ) are provided on opposite sides of the drawbar 5 at aportion of the drawbar located behind the neck portion 7, wherein theseplanar wall sections 5 c, 5 d are in sliding contact with a respectiveplanar surface 3 c, 3 d in the bore 3 in order to prevent mutualrotation between the drawbar 5 and the housing 2. However, mutualrotation between the drawbar 5 and the housing 2 could be prevented inany other suitable manner.

A mounting portion 10 for receiving a mounting shank 61 on the toolholder 60 is provided at a front end of the bore 3. This mounting shank61 is here referred to as tool holder shank.

In the illustrated embodiment, the housing 2 comprises a base part 12and an end piece 13 mounted to the base part 12 at the front end 2 a ofthe housing. The end piece 13 has the form of a sleeve with an axialthrough hole that forms part of the above-mentioned bore 3. In thiscase, the above-mentioned mounting portion 10 is located in the throughhole of the end piece 13. As an alternative, the part of the housing 2accommodating the bore 3 could be formed in one piece without any endpiece of the above-mentioned type.

The tool holder shank 61 is insertable into the mounting portion 10 ofthe bore 3 via the entrance opening 3 a at the front end 2 a of thehousing 2. The head portion 6 of the drawbar is received in anengagement bore 62 in the tool holder shank 61 and a tubular wall 63 ofthe tool holder shank is received in a space between the head portion 6and an inner surface of the end piece 13. In the illustratedembodiments, the mounting portion 10 is conically shaped and has asomewhat “triangular” or polygonal, non-circular cross-sectional shapeadapted to receive a similarly shaped tool holder shank 61. The conicalshape ensures a connection free from play in the radial as well as theaxial direction between the tool holder shank 61 and the housing 2,whereas the non-circular cross-section ensures a non-rotatable fixationof the tool holder shank 61 to the housing 2. However, the mountingportion 10 could also have any other suitable shape for receiving othertypes of tool holder shanks.

Engagement members 20 in the form of segments are arranged around thedrawbar 5 at a front end thereof. Under the effect of a movement of thedrawbar 5 from the advanced releasing position to the retracted lockingposition, the engagement members 20 are moveable from a first position(see FIG. 5 ), in which the engagement members 20 allow the tool holdershank 61 to move into and out of the mounting portion 10 of the bore 3,to a second position (see FIGS. 2 and 4 ), in which the engagementmembers 20 are in locking engagement with an engagement groove 64 in theengagement bore 62 in the tool holder shank 61 and thereby keep the toolholder shank 61 secured to the housing 2.

In the illustrated embodiment, the engagement members 20 are arrangedaround the neck portion 7 of the drawbar 5 and held in place around theneck portion by means of a retainer ring 21 and an elastic O-ring 22,which are arranged in the bore 3 and surround the neck portion 7. Eachengagement member 20 has an outwardly facing flange portion 23 engagedin an inner groove in the retainer ring 21. The O-ring 22 is received inan outwardly facing groove at the rear end of each engagement member 20.A compression spring 24 is also arranged in the bore 3 and configured tosurround the drawbar 5. The compression spring 24 is mounted between ashoulder on the drawbar 5 and the retainer ring 21 and it is configuredto urge the retainer ring 21 and the engagement members 20 forwards. Theforward movement of the retainer ring 21 towards the entrance opening ofthe bore 3 is limited by a shoulder 25 provided in the bore 3. In theillustrated example, this shoulder 25 is formed by a rearwardly facingend surface of the end piece 13.

At its front end, each engagement member 20 is provided with anoutwardly directed engagement flange 27, which is configured to be inengagement with the engagement groove 64 in the tool holder shank 61when the engagement member 20 is in the above-mentioned second position.When the drawbar 5 is in the advanced releasing position, the front endsof the engagement members 20 are located behind the head portion 6 ofthe drawbar 5 and the engagement flanges 27 are out of engagement withthe engagement groove 64 in the tool holder shank 61, as illustrated inFIG. 5 . When the drawbar 5 is moved axially rearwards in the bore 3along the longitudinal axis L thereof, the bevelled surface 8 on thehead portion 6 of the drawbar will come into contact with the front endsof the engagement members 20, wherein the front ends of the engagementmembers 20 will slide on this bevelled surface 8 and be pressed outwardsso that the engagement flanges 27 on the engagement members come intoengagement with the engagement groove 64 in the tool holder shank 61,whereupon the tool holder shank 61 will be pulled by the drawbar 5 intofirm contact with inner surfaces of the end piece 13 at theabove-mentioned mounting portion 10.

The clamping device 1 further comprises an actuating sleeve 30, which isarranged around a peripheral wall 14 of the housing 2 and slidablymounted to this peripheral wall 14 so as to be axially moveable inrelation to the housing 2 along the longitudinal axis L. The actuatingsleeve 30 is non-rotatably mounted to the housing 2, i.e. prevented fromrotating in relation to the peripheral wall 14. In the illustratedexample, balls 15 (see FIGS. 7 and 8 ) are arranged between theactuating sleeve 30 and the housing 2. The balls 15 are distributed inthe circumferential direction of the peripheral wall 14 and each ball 15is accommodated partly in a recess in the peripheral wall 14 and partlyin a longitudinal groove 38 in the actuating sleeve 30. The balls 15 arefixed in axial position in relation to the peripheral wall 14 by beingreceived in the recesses on the outer side of the peripheral wall. Theballs 15 are slidably received in the longitudinal grooves 38 on theinner side of the actuating sleeve 30, and the actuating sleeve 30 isthereby allowed to move axially in relation to the balls 15 when theactuating sleeve is axially moved in relation to the peripheral wall 14.The balls 15 prevent mutual rotation between the actuating sleeve 30 andthe peripheral wall 14.

One or more first wedges 40 are mounted to the housing 2 and configuredto transfer an axial movement of the actuating sleeve 30 in a firstaxial direction D1 in relation to the housing 2 into a movement of thedrawbar 5 from the advanced releasing position to the retracted lockingposition. Furthermore, one or more second wedges 50 are mounted to thehousing 2 and configured to transfer an axial movement of the actuatingsleeve 30 in an opposite second axial direction D2 in relation to thehousing 2 into a movement of the drawbar 5 from the retracted lockingposition to the advanced releasing position. In the illustratedembodiment, the first axial direction D1 is a direction towards thefront end 2 a of the housing 2 and the second axial direction D2 adirection towards the rear end 2 b of the housing 2. Thus, in this casea movement of the drawbar 5 from the advanced releasing position to theretracted locking position is effected by an axial movement of theactuating sleeve 30 forwards along the peripheral wall 14, whereas amovement of the drawbar 5 from the retracted locking position to theadvanced releasing position is effected by an axial movement of theactuating sleeve 30 rearwards along the peripheral wall 14. However, asan alternative, the actuating sleeve 30 and the first and second wedges40, 50 could be arranged to co-operate in such a manner that a movementof the drawbar 5 from the advanced releasing position to the retractedlocking position is effected by an axial movement of the actuatingsleeve 30 rearwards along the peripheral wall 14, and in such a mannerthat a movement of the drawbar 5 from the retracted locking position tothe advanced releasing position is effected by an axial movement of theactuating sleeve 30 forwards along the peripheral wall 14. Thus, in thelatter case, the first axial direction D1 is a direction towards therear end 2 b of the housing 2 and the second axial direction D2 adirection towards the front end 2 a of the housing 2.

In the illustrated embodiment, the clamping device 1 comprises threefirst wedges 40, which are spaced apart in the circumferential directionof the peripheral wall 14. Each first wedge 40 is slidably received in arespective first aperture 45 that extends radially through theperipheral wall 14. The first wedges 40 are configured to jointly pressthe drawbar 5 towards the retracted locking position when they arepressed radially inwards in the associated first apertures 45.

The clamping device 1 may comprise any suitable number of first wedges40 arranged to extend through a corresponding number of first apertures45 in the peripheral wall 14 of the housing 2. The first wedges 40 andthe associated first apertures 45 are preferably evenly distributed inthe circumferential direction of the peripheral wall 14.

Each first wedge 40 comprises a first pressure receiving surface whichfaces outwards from the peripheral wall 14 of the housing 2, and theactuating sleeve 30 is on its inner side provided with first pressureapplying surfaces 31 which face inwards for contacting the firstpressure receiving surfaces 41 on the first wedges. Each first pressureapplying surface 31 has a radial distance to the longitudinal axis Lthat increases as seen in the above-mentioned first axial direction D1.The first pressure applying surfaces 31 are configured to press thefirst wedges 40 radially inwards in the first apertures 45 by pressingagainst the first pressure receiving surfaces 41 on the first wedgeswhen the actuating sleeve 30 is moved in the first axial direction D1.

Each first wedge 40 also comprises a wedge surface 46, which facestowards the rear end 2 b of the housing 2 and which is in contact with afirst slide surface 16 on the drawbar 5 facing towards the front end 2 aof the housing. When the first wedges 40 are pressed radially inwards inthe first apertures 45 by the actuating sleeve 30, the wedge surface 46of each first wedge 40 will slide and press against the correspondingfirst slide surface 16 on the drawbar and thereby force the drawbar 5 tomove towards the retracted locking position.

In the illustrated embodiment, the wedge surface 46 of each first wedgeand the associated first slide surface 16 on the drawbar 5 are formed asplanar surfaces which are inclined in relation to the longitudinal axisL as seen in a longitudinal section through the housing 2 perpendicularto the longitudinal axis L. In this case, these surfaces 16, 46 arelinear as seen in a cross-sectional plane perpendicular to thelongitudinal axis L, as illustrated in FIG. 10 . The wedge surface 46 ofeach first wedge and the associated first slide surface 16 on thedrawbar 5 may as an alternative be curved as seen in a cross-sectionalplane perpendicular to the longitudinal axis L. In the latter case,these surfaces 16, 46 are non-planar. As a further alternative, one ofthese surfaces 16, 46 could be curved as seen in a longitudinal sectionthrough the housing 2 perpendicular to the longitudinal axis L.

The actuating sleeve 30 is preferably configured to assume aself-locking axial position on the peripheral wall 14 when the drawbar 5has been forced into the retracted locking position under the effect ofthe actuating sleeve 30 and the first wedges 40, so as to thereby allowthe actuating sleeve 30 to keep the drawbar 5 in the retracted lockingposition. In the self-locking axial position, frictional forces betweenthe actuating sleeve 30 and parts of the first wedges 40 and/or theperipheral wall 14 that are in contact with the actuating sleeve 30prevent the actuating sleeve from being axially displaced in the secondaxial direction D2.

The first pressure applying surfaces 31 and the first pressure receivingsurfaces 41 are preferably inclined in relation to the longitudinal axisL by such an angle α (see FIG. 4 ) that the first wedges 40 will keepthe actuating sleeve 30 in a self-locking axial position on theperipheral wall 14 when the drawbar 5 has been forced into the retractedlocking position under the effect of the actuating sleeve 30 and thefirst wedges 40.

In the illustrated embodiment, the clamping device 1 comprises threesecond wedges 50, which are spaced apart in the circumferentialdirection of the peripheral wall 14. Each second wedge 50 is slidablyreceived in a respective second aperture 55 that extends radiallythrough the peripheral wall 14. The second wedges 50 are configured tojointly press the drawbar 5 towards the advanced releasing position whenthey are pressed radially inwards in the associated second apertures 55.

The clamping device 1 may comprise any suitable number of second wedges50 arranged to extend through a corresponding number of second apertures55 in the peripheral wall 14 of the housing 2. The second wedges 50 andthe associated second apertures 55 are preferably evenly distributed inthe circumferential direction of the peripheral wall 14.

Each second wedge 50 comprises a second pressure receiving surface 52which faces outwards from the peripheral wall 14 of the housing 2, andthe actuating sleeve 30 is on its inner side provided with secondpressure applying surfaces 32 which face inwards for contacting thesecond pressure receiving surfaces 52 on the second wedges. Each secondpressure applying surface 32 has a radial distance to the longitudinalaxis L that increases as seen in the above-mentioned second axialdirection D2. The second pressure applying surfaces 32 are configured topress the second wedges 50 radially inwards in the second apertures 55by pressing against the second pressure receiving surfaces 52 on thesecond wedges when the actuating sleeve 30 is moved in the second axialdirection D2.

Each second wedge 50 also comprises a wedge surface 57, which facestowards the front end 2 a of the housing 2 and which is in contact witha second slide surface 17 on the drawbar 5 facing towards the rear end 2b of the housing. When the second wedges 50 are pressed radially inwardsin the second apertures 55 by the actuating sleeve 30, the wedge surface57 of each second wedge 50 will slide and press against thecorresponding second slide surface 17 on the drawbar and thereby forcethe drawbar 5 to move towards the advanced locking position.

In the illustrated embodiment, the wedge surface 57 of each second wedgeand the associated second slide surface 17 on the drawbar 5 are formedas planar surfaces which are inclined in relation to the longitudinalaxis L as seen in a longitudinal section through the housing 2perpendicular to the longitudinal axis L. In this case, these surfaces17, 57 are linear as seen in a cross-sectional plane perpendicular tothe longitudinal axis L, as illustrated in FIG. 11 . The wedge surface57 of each second wedge and the associated second slide surface 17 onthe drawbar 5 may as an alternative be curved as seen in across-sectional plane perpendicular to the longitudinal axis L. In thelatter case, these surfaces 17, 57 are non-planar. As a furtheralternative, one of these surfaces 17, 57 could be curved as seen in alongitudinal section through the housing 2 perpendicular to thelongitudinal axis L.

Each first wedge 40 may also comprise a third pressure receiving surface43 which faces outwards from the peripheral wall 14 of the housing 2,wherein the actuating sleeve 30 on its inner side is provided with athird pressure applying surface 33 which faces inwards for contactingthe third pressure receiving surface 43 on each first wedge. The thirdpressure applying surface 33 has a radial distance to the longitudinalaxis L that increases as seen in the first axial direction D1. The thirdpressure applying surface 33 and the third pressure receiving surfaces43 are inclined in relation to the longitudinal axis L by an angle β(see FIG. 6 ) which is larger than the above-mentioned angle α. Thefirst and third pressure applying surfaces 31, 33 and the first andthird pressure receiving surfaces 41, 43 are arranged consecutively onthe actuating sleeve 30 and on each first wedge 40, respectively, suchthat, upon a movement of the actuating sleeve 30 in the first axialdirection D1, the third pressure applying surface 33 is configured toslide and press against the associated third pressure receiving surfaces43 during an initial first phase of the movement, whereupon the firstpressure applying surfaces 31 are configured to slide and press againstthe associated first pressure receiving surfaces 41 during a subsequentsecond phase of the movement.

In the illustrated embodiment, said third pressure applying surface 33on the actuating sleeve 30 has the form of an annular rotationallysymmetric surface. In this case there is one single third pressureapplying surface 33 on the actuating sleeve 30. However, the actuatingsleeve 30 could as an alternative be provided with several separatethird pressure applying surfaces 33 corresponding to the number of firstwedges 40, wherein the third pressure receiving surface 43 on each firstwedge 40 is associated with its own third pressure applying surface 33on the actuating sleeve 30.

The first and third pressure applying surfaces 31, 33 and the first andthird pressure receiving surfaces 41, 43 are with advantage curved asseen in a cross-sectional plane perpendicular to the longitudinal axisL. Also the second pressure applying surfaces 32 and the second pressurereceiving surfaces 52 may be curved as seen in a cross-sectional planeperpendicular to the longitudinal axis L. However, one or more of thepressure applying surfaces 31, 32, 33 and pressure receiving surfaces41, 52, 43 may as an alternative have the form of planar surfaces andconsequently be linear as seen in a cross-sectional plane perpendicularto the longitudinal axis L. In the illustrated embodiment, each secondpressure applying surface 32 is provided in a recess 34 formed in arotationally symmetric inner wall surface 35 of the actuating sleeve 30.Furthermore, in the illustrated embodiment, a portion 39 of thisrotationally symmetric inner wall surface 35 on the inner side of theactuating sleeve is conically shaped and the first pressure applyingsurfaces 31 are provided on different parts of this conically shapedwall portion 39.

The first wedges 40 and the second wedges 50 are preferably alternatelyarranged as seen in the circumferential direction of the peripheral wall14, wherein each one of the first wedges 40 is followed by one of thesecond wedges 50 as seen in the circumferential direction of theperipheral wall 14 and each one of the second wedges 50 is followed byone of the first wedges 40 as seen in the circumferential direction ofthe peripheral wall 14.

In the illustrated embodiment, the first pressure applying surfaces 31and the second pressure applying surfaces 32 partly overlap each otherin the axial direction of the actuating sleeve 30 and they are spacedapart from each other in the circumferential direction of the actuatingsleeve 30.

The first and second wedges 40, 50 are non-rotatably received in theassociated first and second apertures 45, 55 in the peripheral wall 14of the housing 2, i.e. each wedge is prevented from rotating in theassociated aperture. In the illustrated embodiment, each wedge 40, 50and the associated aperture 45, 55 in the peripheral wall 14 have mutualcontact surfaces with a circular cross-sectional shape. In this case, aball 18 (see FIGS. 10 and 11 ) is arranged between each wedge 40, 50 andthe inner surface of the associated aperture 45, 55, wherein this ball18 is accommodated partly in a recess 48, 58 in an envelope surface ofthe wedge and partly in an elongated groove 19 in the inner surface ofthe aperture. The ball 18 remains fixed in position in relation to theassociated wedge 40, 50 by being received in the recess 48, 58 on theenvelope surface thereof. The ball 18 is slidably received in theelongated groove 19 in the associated aperture 45, 55, and the wedge 40,50 is thereby allowed to move in the axial direction of the associatedaperture 45, 55 at the same time as the ball 18 prevent the wedge fromrotating in the aperture. As an alternative, the envelope surfaces ofthe wedges 40, 50 and the inner surfaces of the apertures 45, 55 couldhave a non-circular cross-sectional shape, for instance an ovalcross-sectional shape, in order to prevent the wedges from rotating inthe associated apertures.

The clamping device 1 may also comprise additional components, such asone or more hydraulic of pneumatic actuators, for effecting the movementof the actuating sleeve 30 in the first and second axial directions D1,D2. The control of the clamping device 1 may easily by automatized bymeans of such an actuator. Thus, the clamping device 1 according to thepresent invention is suitable for use in automatic tool changingoperations. However, the clamping device 1 according to the presentinvention may also be adapted for manual operation.

When a tool holder 60 is to be clamped to the housing 2, the tool holdershank 61 is inserted into the mounting portion 10 of the bore 3 with thedrawbar 5 positioned in the advanced releasing position, as illustratedin FIG. 5 . Hereby, the head portion 6 of the drawbar is received in theengagement bore 62 in the tool holder shank 61 and the engagement groove64 in the tool holder shank 61 is positioned on the outside of theengagement flanges 27 of the engagement members 20. Thereupon, theactuating sleeve 30 in moved in the first axial direction D1, forinstance by means of a hydraulic or pneumatic actuator or manualoperation. During a first phase of this axial movement of the actuatingsleeve 30, the third pressure applying surface 33 on the actuatingsleeve 30 will slide and press against the third pressure receivingsurfaces 43 on the first wedges 40. Hereby, the first wedges 40 will bepressed radially inwards and the drawbar 5 will be axially displacedtowards the retracted locking position. Due to the relatively steepinclination 13 of the third pressure applying and receiving surfaces 33,43, the first wedges 40 will initially move inwards rather fast, whichresults in a relatively quick displacement of the drawbar 5. Therelatively steep angle β is advantageous since the initial displacementof the drawbar 5 does not require much force. The first and thirdpressure applying surfaces 31, 33 and the first and third pressurereceiving surfaces 41, 43 are so arranged that when the actuating sleeve30 has been moved such a distance that the third pressure applyingsurface 33 has passed the third pressure receiving surface 43 and thefirst pressure applying surface 31 reaches the first pressure receivingsurface 41, i.e. at the transition between these respective surfaces,the drawbar 5 has almost reached its final retracted position in thebore 3. Hence, for the final clamping phase, in which a large force isbeneficial, the first pressure applying and receiving surfaces 31, 41are active. In this phase, a relatively large movement of the actuatingsleeve 30 will result in a very small radial displacement of the firstwedges 40, and an even smaller axial displacement of the drawbar 5,which consequently will provide a force amplifying effect that will makeit possible for the drawbar 5 to pull the tool holder shank 61 with alarge force into firm engagement with the housing 2. Furthermore, thesmall inclination a of the first pressure applying and receivingsurfaces 31, 41 will provide a self-locking effect and make sure thatthe clamping device will remain in the clamped state without requiringany additional locking means. Hereby, the force on the actuating sleeve30 may be released when the drawbar 5 has reached the retracted lockingposition.

When a tool changing operation is to be performed and the tool holder 60is to be released from the housing 2, the actuating sleeve 30 is movedin the second axial direction D2. When the actuating sleeve 30 issubjected to a sufficient force in the second axial direction D2, theself-locking frictional engagement between the first pressure applyingsurface 31 on the actuating sleeve 30 and the first pressure receivingsurfaces 41 on the first wedges 40 will be released, whereupon theactuating sleeve 30 is moveable in relation to the housing 2 in thesecond axial direction. When the actuating sleeve 30 is moved in thisdirection, the second pressure applying surfaces 32 on the actuatingsleeve 30 will slide and press against the second pressure receivingsurfaces 52 on the second wedges 50.

Hereby, the second wedges 50 will be pressed radially inwards and thedrawbar 5 will be axially displaced towards the advanced releasingposition. When the drawbar 5 is moved towards the advanced releasingposition, the outer end of the head portion 6 of the drawbar 5 will hitagainst a surface 65 in the engagement bore 62 in the tool holder shank61 and thereby release the tool holder shank 61 from the housing 2.During the movement of the drawbar 5 towards the advanced releasingposition, the first slide surfaces 16 on the drawbar 5 are pressedagainst the wedge surfaces 46 on the first wedges 40 and will therebypress the first wedges 40 radially outwards. The movement of the firstwedges 40 in radial direction outwards is limited by a stop ring 36,which is fixed in an annular groove 37 on the inner side of theactuating sleeve 30.

The invention is of course not in any way restricted to the embodimentsdescribed above. On the contrary, many possibilities to modificationsthereof will be apparent to a person with ordinary skill in the artwithout departing from the basic idea of the invention such as definedin the appended claims.

1. A clamping device for releasably holding a tool holder shank, theclamping device comprising: a housing having a front end, a rear end anda bore which intersects the front end and extends rearwardly therefrom,wherein a mounting portion for receiving the tool holder shank isprovided at a front end of the bore; a drawbar slidably mounted insidethe bore so as to be reciprocally moveable in the bore along alongitudinal axis thereof between an advanced releasing position and aretracted locking position; engagement members arranged around thedrawbar at a front end thereof, wherein the engagement members, underthe effect of a movement of the drawbar from the advanced releasingposition to the retracted locking position, are moveable from a firstposition, in which the engagement members allow the tool holder shank tomove into and out of said mounting portion, to a second position, inwhich the engagement members are in locking engagement with the toolholder shank and keep it secured to the housing; and a first wedgehaving a wedge surface facing towards the rear end of the housing and afirst pressure receiving surface, wherein the first wedge is slidablyreceived in a first aperture that extends radially through a peripheralwall of the housing, wherein the first pressure receiving surface on thefirst wedge faces outwards from the housing and the wedge surface on thefirst wedge is in contact with a first slide surface on the drawbarfacing towards the front end of the housing, the first wedge beingconfigured to press the drawbar towards the retracted locking positionwhen it is pressed radially inwards in the first aperture; that theclamping device including a second wedge slidably received in a secondaperture that extends radially through the peripheral wall, wherein thesecond wedge includes a second wedge surface, which faces towards thefront end of the housing and is in contact with a second slide surfaceon the drawbar facing towards the rear end of the housing, and a secondpressure receiving surface, which faces outwards from the housing, thesecond wedge being configured to press the drawbar towards the advancedreleasing position when it is pressed radially inwards in the secondaperture, wherein the clamping device includes an actuating sleevearranged around the peripheral wall and slidably mounted to it so as tobe axially moveable in relation to the housing in a first axialdirection in order to effect a movement of the drawbar from the advancedreleasing position to the retracted locking position and in an oppositesecond axial direction in order to effect a movement of the drawbar fromthe retracted locking position to the advanced releasing position,wherein the actuating sleeve on its inner side is provided with a firstpressure applying surface, which faces inwards for contacting the firstpressure receiving surface and has a radial distance to the longitudinalaxis that increases as seen in said first axial direction, and a secondpressure applying surface, which faces inwards for contacting the secondpressure receiving surface and has a radial distance to the longitudinalaxis that increases as seen in said second axial direction, wherein thefirst pressure applying surface is configured to press the first wedgeradially inwards in the first aperture by pressing against the firstpressure receiving surface when the actuating sleeve is moved in saidfirst axial direction and wherein the second pressure applying surfaceis configured to press the second wedge radially inwards in the secondaperture by pressing against the second pressure receiving surface whenthe actuating sleeve is moved in said second axial direction.
 2. Theclamping device according to claim 1, wherein the actuating sleeve isconfigured to assume a self-locking axial position on the peripheralwall when the drawbar has been forced into the retracted lockingposition under the effect of the actuating sleeve and the first wedge,so as to thereby keep the drawbar in the retracted locking position. 3.The clamping device according to claim 2, wherein the first pressureapplying surface and the first pressure receiving surface are inclinedin relation to the longitudinal axis by such an angle α that the firstwedge will keep the actuating sleeve in a self-locking axial position onthe peripheral wall when the drawbar has been forced into the retractedlocking position under the effect of the actuating sleeve and the firstwedge.
 4. The clamping device according to claim 3, wherein the firstwedge comprises includes a third pressure receiving surface which facesoutwards from the housing, wherein the actuating sleeve on its innerside is provided with a third pressure applying surface, which facesinwards for contacting the third pressure receiving surface, the thirdpressure applying surface having a radial distance to the longitudinalaxis that increases as seen in said first axial direction, wherein thethird pressure applying surface and the third pressure receiving surfaceare inclined in relation to the longitudinal axis by an angle β, whichis larger than the angle and wherein the first and third pressureapplying surfaces and the first and third pressure receiving surfaces,are arranged consecutively on the actuating sleeve and on the firstwedge, respectively, such that, upon a movement of the actuating sleevein the first axial direction, the third pressure applying surface isconfigured to slide and press against the third pressure receivingsurface during a first phase of the movement and the first pressureapplying surface is configured to slide and press against the firstpressure receiving surface during a subsequent second phase of themovement.
 5. The clamping device according to claim 1, wherein the firstand third pressure applying surfaces and the first and third pressurereceiving surfaces are curved as seen in a cross-sectional planeperpendicular to the longitudinal axis.
 6. The clamping device accordingto claim 1, wherein the first pressure applying surface and the secondpressure applying surface partly overlap each other in the axialdirection of the actuating sleeve and are spaced apart from each otherin the circumferential direction of the actuating sleeve.
 7. Theclamping device according to claim 6, in that wherein the secondpressure applying surface is provided in a recess formed in arotationally symmetric inner wall surface of the actuating sleeve. 8.The clamping device according to claim 1, characterized in that whereinthe clamping device comprises includes two or more first wedges spacedapart in the circumferential direction of the peripheral wall, eachfirst wedge being received in a respective first aperture that extendsradially through the peripheral wall.
 9. The clamping device accordingto claim 8, wherein the first wedges are three in number.
 10. Theclamping device according to claim 8, said wherein the first wedges areevenly distributed in the circumferential direction of the peripheralwall.
 11. The clamping device according to claim 8, wherein the clampingdevice includes two or more such second wedges spaced apart in thecircumferential direction of the peripheral wall, each second wedgebeing received in a respective second aperture that extends radiallythrough the peripheral wall.
 12. The clamping device according to claim11, said wherein the second wedges are three in number.
 13. The clampingdevice according to claim 11, said wherein the second wedges are evenlydistributed in the circumferential direction of the peripheral wall. 14.The clamping device according to claim 11, wherein the first wedges andthe second wedges are alternately arranged as seen in thecircumferential direction of the peripheral wall, wherein each one ofthe first wedges is followed by one of the second wedges as seen in thecircumferential direction of the peripheral wall and each one of thesecond wedges is followed by one of the first wedges as seen in thecircumferential direction of the peripheral wall.
 15. The clampingdevice according to claim 1, wherein the housing is a machine spindle.